Apparatus for coating a nonmetallic fibre with a metal



Dec. 30, 1969 n. mnsvwoon I 3,486,480

APPARATUS FOR COATING A NONMETALLIC FIBRE WITH A METAL .F'iled Oct. 25,1.968

In venlor I Dav/n MAIN Hiywaoo By WW, W Attorneys United States PatentInt. ci. Bc 3/12 US. Cl. 118-401 2 Claims ABSTRACT OF THE DISCLOSURE Theinvention relates to metal coating of nonmetallic, e.g. silica, fibresby continuously passing the fibre through a slot in a nozzle having atleast two axial passageways, the fibre passing through the slottransversely of the axes of the passageways. Molten metal is suppliedthrough the passageways to the slot where it coats the fibre. The fibreis surrounded with a non-oxidising atmosphere after coating, and isexposed to oxygen at the entry thereof to the slot.

This invention concerns an apparatus for coating a nonmetallic fibrewith a metal, and is a continuation-inpart of my application No.425,775, filed Jan. 15, 1965, now abandoned.

According to the present invention there is provided an apparatus forcoating a nonmetallic fibre with a metal comprising a reservoir adaptedto contain molten metal, a coating chamber, means for supplying the saidcoating chamber with an atmosphere containing less than 5% oxygen byweight, a nozzle formed with substantially axial passage means throughwhich molten metal from the reservoir is continuously discharged inoperation, and a slot defined in said nozzle which has a fibre-entry endand a fibre-exit end and which intersects said passage means at asubstantial angle, and means for drawing said fibre through said slot,said nozzle being so mounted that said fibre-exit end is positionedwithin the said coating chamber for communication therewith while saidfibre entry end is positioned externally of the said coating chamber andcommunicates with normal atmosphere.

Preferably the said passage means includes at least two passagewayswhich are substantially parallel and which communicate with each other.

The metal may be aluminium or an aluminium alloy, or indeed any metal oralloy e.g. cadmium which is prone to oxidation in air when in the moltenstate.

The fi-bre may be a silica fibre. Thus the fibre may be drawn from a rodof fused silica and through a high temperature flame. The flame mayarise from the combustion of oxygen and coal gas.

The invention is illustrated, merely by way of example, in theaccompanying drawings, in which:

FIGURE 1 is a diagrammatic sectional view of apparatus according to thepresent invention for coating a nonmetallic fibre with a metal,

FIGURE 2 is a section on an enlarged scale taken on the line 22 ofFIGURE 1.

Referring to the drawings, an apparatus for coating a fibre with a metalcomprises a reservoir which is adapted to contain molten metal 11 andwhich is provided with an outlet duct 12. The molten metal 11 may bepure aluminium or may be an aluminium alloy containing 0.01% bismuth byweight. Means (not shown) are provided for keeping the metal 11 in thereservoir 10 molten.

3,486,480 Patented Dec. 30, 1969 A substantially semi-cylindricalcoating chamber 13 has an upper wall 28 which as a coating nozzle 14mounted centrally therein. The nozzle 14 has two substantially parallelducts or axial passageways 15, 16 which communicate with each other, andeach of which communicates with the outlet duct 12. Thus the passageways15, 16 are arranged to receive molten metal from the reservoir 10. Thenozzle 14 is also provided with a slot 17 which has an upper fibre-entryend and a lower fibre-exit end which communicates with the passageways15, 16. The wall 28 is bolted to the remainder of the chamber 13 bybolts 29.

A rod of fused silica 20' is clamped in position by support members 21.Disposed adjacent the lower end of the rod 20 is a torch 22 which issupplied with oxygen and coal gas by means not shown. The flame from thetorch 22 softens the lower end of the rod 20 and permits a fibre 23 tobe drawn by hand from the lower end of the rod 20.

Alternatively, the fibre 23 may be drawn from a source (not shown) ofmolten silica, or the fibre 23 may be a previously formed silica fibre.

The fibre 23 is passed through the flame from the torch 22 and throughthe slot 17 and is then wound around a take-up roller 24. The fibre 23,in passing through the slot 17, becomes coated with the metal 11.

The coating chamber 13 communicates by way of a pipe 25 with a bottle 26of a gas such for example as nitrogen or any one or more of the gasesargon, hydrogen, helium, carbon dioxide, carbon monoxide, hydrogensulphide, ammonia or chlorine. The pipe 25 may be provided with a valve(not shown) for controlling flow therethrough and with a flow meter (notshown).

The fibre 23, in passing through the slot 17, will sometimes pick up asac 27 of aluminium. It has been found that fibres coated with metalwith the apparatus described so far, but without the use of a protectiveatmosphere of any sort, have a matt grey appearance when viewed from adistance and have, at irregular intervals along their length, sphericalblobs. These blobs grow near the apex of a conical sac of metal whichforms under the tip of the coating nozzle and through which the fibrepasses.

Blob formation is believed to be due to the presence of an oxide skin onthe sac of metal (e.g. aluminium). The movement of a coated fibre downthe sac will tend to set up a circulation in the aluminium giving riseto a tension in the alumina skin which surrounds the sac. This tensionwill vary considerably and will be affected by a number of factors, butit will from time to time be suflicient to rupture the alumina skin andallow the outflow of some metal. Once outside the sac, the aluminium isnot affected by the movement of the fibre and is free to take up aspherical form. A blob may then grow until it reaches the apex of thesac when the moving fibre will interfere with its growth and tear theblob off. Alternatively, the original rupture may increase in size untilthe sac is so weakened that it cannot support the weight of the blob.

The above theoretical explanation suggests that if formation of theoxide could be suppressed, the formation of blobs might be prevented.This was found to be the case if an inert gas blanket was maintainedover and around the entire coating nozzle, but it was found that, in atypical example, the fibre strength dropped from 450 kg./mm. for theblobby fibre to only kg./ min? for the blob-free material.

It has been postulated that the explanation for this phenomenon is thatthe inert gas blanket excludes the oxygen from the molten aluminium andprevents the formation of a protective skin of alumina which wouldotherwise be continuously drawn down between the aluminium and thesilica fibre as the fibre enters the coating nozzle.

Accordingly, and with particular reference to FIG- URE 2, the protectiveatmosphere is provided to cover only the bottom half of the coatingnozzle 14. Thus it will be seen that the upper or fibre-entry end of theslot 17 is open to normal atmosphere and the aluminium is thus allowedto oxidise and form a protective alumina skin on the fibre. Experimentshave confirmed this and mean strengths of 563 l g./mm.- have beenrecorded on small batches of coated fibres.

The protective atmosphere is thought also to make a contribution to highstrength by acting as a constant temperature enclosure and by preventingdraughts from aifecting the coating nozzle temperature. The compositionof the protective atmosphere was found not to be critical, provided itwas substantially oxygen-free, i.e. contained less than 5% oxygen byWeight. It was also found that the coated fibres had a lustrousappearance.

I claim:

1. Apparatus for coating a nonmetallic fibre with a metal comprising areservoir adapted to contain molten metal, a coating chamber, means forsupplying the said coating chamber with an atmosphere containing lessthan 5% oxygen by weight, a nozzle formed with substantially axialpassage means through which molten metal from the reservoir iscontinuously discharged in operation, said passage means including atleast two passageways which are substantially parallel and whichcommunicate with each other, and a slot defined in said nozzle which hasa fibre-entry end and a fibre-exit end and which intersects said passagemeans at a substantial angle, and means for drawing saidfibre throughsaid slot, said nozzle being so mounted that said fibre exit end andsubstantially all of the delivery end of said parallel passageways arepositioned within the said coating chamber for communication therewithWhile said fibre entry end is positioned externally of the said coatingchamber and communicates with normal atmosphere.

2. Apparatus as claimed in claim 1 wherein the coating chamber issubstantially semi-cylindrical, the said coating nozzle being mountedsubstantially centrally of its planar wall.

References Cited UNITED STATES PATENTS 2,526,731 10/1950 Coburn 118-420X 3,001,507 9/1961 Whitehurst et al. 3,347,208 10/ 1967 Arridge 118-420MORRIS KAPLAN, Primary Examiner

